The informant, who used to work at the Swiss arm of the British bank, HSBC, has offered to sell the data to the government for €2.5m (£2.2m) Experts say the information, which is contained on a CD, could reap up to €200m (£174.60m) in tax revenue.

Despite strong voices of opposition within her own party, Merkel said: "Our goal should be to obtain this data, if it is relevant.

"We should try everything to get information on possible tax evaders. Every reasonable person knows that tax evasion needs to be uncovered."

But Swiss president Doris Leuthard hit back, saying it was "insidious" for a state that operates under the rule of law "to make use of illegal data".

Merkel's willingness to buy the data, which has rattled relations between Germany and Switzerland, already at odds over the controversial issue of banking secrecy, was in contrast to members of her own conservative Christian Democratic Union (CDU) and its sister party the CSU. Several spoke out against buying the stolen data at the weekend, saying it was morally questionable to use it to ensnare potential tax evaders.

Opposition politicians accused the conservatives of trying to protect their own interests as they pushed for the government to buy the data.

An estimated €175bn is held in Swiss bank accounts by German citizens.

A spokesman for the German finance minister, Wolfgang Schäuble, said before any decision was made it would be necessary to "establish legal clarity" over using illegally acquired data.

Thomas Sutter, the spokesman for the Swiss Bankers Association, cautioned Germany over acquiring "stolen property". He said he did not believe that the German government "would want to be seen as the recipient of stolen goods" and warned that "if Switzerland was put under pressure", it could be "counterproductive" for current negotiations between the two countries over a new double taxation treaty.

Schäuble's spokesman warned that if the government bought the data, it could "severely shake" the relationship between the two countries.

But it said the precedent had been set two years ago when Germany purchased stolen bank data from the former employee of a bank in Liechtenstein and used it to pursue tax evaders. The information, for which it paid €4.2m, included data on around 600 Germans, the most prominent of whom was Klaus Zumwinkel, the former CEO of Deutsche Post. Zumwinkel was subsequently fined €1m in tax evasion charges and given a two-year suspended prison sentence.

The alleged seller of information this time has been named as the 37-year- old former HSBC banker, and French citizen, Hervé Falciani, who is believed to have also offered bank data to the French authorities last August.

German authorities involved in the investigation said from the samples of the data they had seen they had no doubt it was authentic.

Joachim Poss, the deputy chief whip of the opposition Social Democrats urged the conservatives and their junior coalition party, the Free Democrats, to act objectively, and to not attempt to "protect the interest of their own voters who are on the whole the owners of larger fortunes".